Heater for rods and tubes



March 7, 1933 E. F. NoR'rHnuP HEATER FOR RODS AND TUBES Filed Dec. 21,X925 2 Sheets-Sheet jf' e9 J6 J! M l mom -w-l 4f 45 JMU/@IMM March 7,1933. E. F. NoRTHRuP HEATER FOR RODS AND TUBES 2 Sheets-Sheet 2 FiledDec. 21, 1925 Patented Mar. 7, 1933 UNITED STATES PATENT OFFICE EDWIN F.NORTHRUP, OF NEAR PRINCETON, NEW JERSEY, ASSIGNOB T0 AJAX ELEG-TBJTHERMIG OORPORTION, 0F TRENTON, N'EW JERSEY, A CORPORATION Ol* NIWJERSEY HEATER FOR RODS AND TUBES Application led December 21, 1925.Serial No. 78.878.

My invention relates to the inductive heating of solid and tubulararticles both fixed and movable and to apparatus by which these methodsmay be practiced.

One of the purposes of my invention is to surround solid or tubulararticles with a conductor through which high frequency current is to bepassed and to heat them by the current induced preferabl while they arepassing through the coils ut ermissibly during stops in step-by-ste feeing.

A further urpose is to app y induction to a moving rod or tube by a coilor coils surrounding the rod or tube and through which current is passedhavin a frequenc above normal frequencies an a correcte power factor. p

A further purpose is to provide parallel coils or turns all fed from thesame source of high frequency current and all operatin successively uponthe same tube or rod fe through them for the urpose of addingsuccessively increments o? heat to the rod, strip or tube passingthrough them.

A further purpose is to heat a magnetic rod, strip or tube by successiveincrements from induction at different frequencies.

A further purpose is to use a relatively low frequency for inductiveheating of rods, strips or tubes of magnetic material up to nearly thepoint at which they lose this roperty, to heat them beyond this point ya higher frequency using the same inductor or part of the same inductorfor both, either at the same time or separate times.

A further purpose is to supply part of the inductor for a heating systemfrom a line from which a synchronous motor is driven, to provide excessKVA in the synchronous motor in order to correct the power factor ofthis portion of the inductor and to supply the remainder of the inductorfrom a generator driven by the synchronous motor and having the powerfactor corrected by condensers.

A further purposeis to correct the powerfactor of alternating currentcoils carrying high frequency current and forming a plu'- ra ity ofheating zones, performing part of the heating function cumulatively ineach of successive zones.

A further purpose is to provide a plurality of inductors in serieswithin the same secondary winding, preferably with the axes of theirzones of inductance parallel.

Further urposes will appear in the specification and in the claims.

I have preferred to illustrate a few forms only among many in which myinvention may appear, selecting forms which best illustrate theprinciples of my invention.

Figure 1 is a longitudinal section of one form of inductor applied to atravelling bar or rod.

Figure 2 is a section of Figure 1 taken upon line 2 2.

Figures 3, 4, 5, 6, 7, 8 and 9 are diagrammatic forms showing d-ierentcircuit connections.

Figure 10 is a longitudinal section showing a core anchorage.

Figures 11 and 12 are perspective views lar ely diagrammatic showingmullles.

igure 13 is a side sectional perspective showing another form.

Figure 14 is an elevation corresponding to section 14--14 of Figure 13but showing a plurality of conductors to the single turn.

In the drawing similar numerals indicate like parts.

Though I prefer to operate at a higher frequency than that of existingcurrent supplies and gain considerable advantage from this, features ofmy invention are of advantage whatever the frequency and are claimedaccordingly.

In Figures 1 to 9 I have shown diierent ways in which current at morethan normal frequency can be supplied to an inductor comprising a singlecoil or spaced coils operating upon the same moving bar, rod, strlp ortube of regular or irregular shape, or to a conducting content, to raiseit to the reclpeired temperature as for rivet heating, tu or stripannealing or for other operations. By these different illustrations Ihave intended to indicate that the application of abnormal frequency tothis duty involves invention 1n addition to whatever merit may lie inthe manner of applying it.

In Figures 1 and 2 I have shown a method of integratin the heatingeffects of successive coils t rough which high fre uency current ispassed in the heating of a ar or rod which is advanced to progresseither continuously or intermittently as preferred, as by a set ofrollers 20 and 21 suitably mounted and one of them driven by anysuitable gearing, here typified by gears 22 and 23 of which 23 is on thesame shaft as the feed rollers 21. The coils 24, 25, 26, 27 and 28 arehere shown as helical coils nearly fitting the bar, wire, rod or strip29 of which a section 30 has just been cut for use. I have notconsidered it necessary to illustrate the protecting covers forpreventing undue cooling of the bar etc., between the coils, as thesecould exist in great variety. The coils could be water-cooled if desiredas in the case of the annular coils shown in my patents.

The coils are shown as separate and as separately supplied with highfrequency current through transformers 31 whose primaries receivecurrent at existing freuencies. The secondaries are connected to t ecoils through condensers 32 which when charged discharge across gaps 33.They can be one long coil or a series of coils dependinv upon the rateof speed of the charge.

uch a mechanism as described is suitable, for example, for heating abar, rod, strip or wire from which nails or spikes are to be made andthe one portion 3() of the bar or rod is separated as would be the casein the making of spikes. Both hysteresis and eddy currents may bepresent and the bar, rod, strip or wire would be delivered continuouslyor intermittently to the cutting mechanism of the nail or spike machineat any temperature designed, as required for the head- 1n mechanism.

t will be evident that the methods and mechanism herewith are capable ofuse generally or to heat treat electrically conducting objects in motionor which are moved step by step between treatments, whether they bemagnetizable or not; and that the treatment may be applied to thespecial form of objects to be treated by accommodation of the coils inshape to these forms. The materials primarily to be treated when notelectrically conducting may be treated by mounting them on or incasingthem within electrically conductin objects in which the heat is developeMufiie heating is claimed by me in a separate application.

Whereas in Figures 1 and 2the supply of current to the primary of thetransformer may have any frequency such as normal GQ cycle linefrequency, in the structure shown in most of the other diagrammaticfigures direct connection with a generator is contemplated for some atleast of thJ inductor coils, and the frequency chosen will dependlargely upon the temperature to which the charge is to be heated, thedesirability of using direct line current or current from a specialgenerator, and the cost of power factor correction.

lVhere the temperature intended to be reached is below the point atwhich iron or steel loses its magnetic properties a much lower frequencywill suffice than is required Where the final temperature intended isabove this point, with the result that a choice is offered for thesehigher temperatures betweeniraising the frequency of the entireequipment to a frequency which will be effective above the recallencepoint or raising the temperature in a part of the range required by aninductor operating at one frequency and utilizing another higherfrequency through the same or a separate inductor coil or coils toattain the higher temperatures.

It is very desirable that the frequency shall be high enough so that theenergy induced shall not pass appreciably beyond the center of a solidbar or rod operated upon nor tend to pass appreciably beyond the innerwall of a tube which is being heated, and, as later pointed out, thesize of stock operated upon therefore materially' affects the choice offrequency. However, alternators of the standard rotary multi-polar typeare now available giving frequencies of Well over 500 cycles whichbrings direct supply from the alternators Within the range of frequencymost desirable for present purposes, and frequency changers free frommovable parts have made it possible to double or quadruple thefrequencies without excessive cost and at a low loss in efficiency.

It is my intention to include Within my generator supply such generatorsand such use of frequency changers as may best suit the needs of theindividual installation.

In Figure 3 I show a generator 34 having its power factor correcteddirectly, supplying` an inductor 35 whose positive inductance isbalanced by capacity 32', capable, as in the other illustrations, of anyrequired adjustments. The tube is fed through the inductor continuouslyor intermittently as best suits the purpose for which the tube is heatedand the needs of a particular installation.

The coil in Figure 3 is intended to represent any single turn coil` ormultiple turn coil or combination thereof fed from a singlm cuit andinterrupted if desired for supporting mechanical or other structure asindicated diagrammatically in Figure 4.

Instead of the direct generator shown in Figure 3 and in other figuresherein continuous oscillations can be produced by making use of vacuumelectron tubes, complying With the conditions for obtainingoscillations, in that inductive react-ance (condensers) and positivereactance (inductance coils) are combined in the same circuit. I havenot considered it necessary to illustrate this mode of securing current.

In Figure 5 I have shown direct alternator feed with power factorcorrection for all of the inductor coil sections 36, 37, 38 shown, inconjunction with transformer and discharge gap connections correspondinggenerally with those of Figure 1 for applying high frequency to the lastsection, 38 of the coil. In this case the high frequency is superimposedupon the lower frequency in the same coil. They may be operatedseparately. The primary 39 feeds a high frequency circuit correspondingwith any of the high frequency circuits shown in Figure 1.

In this form stock, Whether solid or tubular, regular or irregular canbe raised to a temperature of say 675O C. in the other coils and islifted in the last coil to say 8000 C. or 1100C C. as may be requiredfor the work intended.

In Figure 6 the lower frequency is used as in Figure 4 for operationupon iron or steel which has lost its magnetic properties, and a Whollyseparate high frequency coil 40 is provided, fed by transformer 4lhaving its prmary 42 across the lower frequency lines and correspondingfrom this point with one of the high frequency circuits shown in Figure1.

In Figure 7 separate lower and higher frequency generators 43 and 43 areprovided, the lower frequency and the higher frequency each supplyingone or a plurality of inductor coil sections 24, 25, 26 and 40 as shownin Figures 3 and 4. The higher frequency has been shown as ultilizing ashorter inductor section as would very possibly be the case.

The form shown in Figure 0 would be used Where the voltage of the supplyline is not high enough to operate the discharge Vtlhere the voltage ofthe generator 43 is high enough to operate the discharge gap 33, thearrangement shown in Figure 8 is permissible. Here part of the inductor24, 25 is supplied directly from the generator, with power factorcorrection. corresponding generally with Figure 3 or Figure 4 and afurther part 40 of the inductor is fed through condensers 32. Suitableinductance 44 and discharge gap 33 complete the circuit.

In the form shown in Figure 9 a threephase current supply at say 60cycles and any desirable voltage, operates a synchronous motor 45driving a generator 46 having any frequency and voltage desired,preferably a much higher frequency and voltage.

From the low frequency circuit inductor coils or sections 3G, 37 and 38are fed. The high frequency generator 46 is also shown as three-phaseand is connected to inductor coils or sections 40', 402 and 403.Condensers are shown to correct the power factor of these coils orsections. All six inductor sections or coils are shown as operating uponthe same charge. in the form of a bar, rod, strip or tube to be heatedby them.

Assuming a power factor initially of thc circuit feeding the synchronousmotor of 50%, if this motor be given an excess KVA the power factor ofthe current supply circuit here Will be corrected to 100%. Since asynchronous motor Will be needed 1n any event for driving the highfrequency generator the additional cost wf doubling the generator KVA isnot nearly as great as for the initial KVA required. This power factorcorrection by excess synchronous motor KVA is in the nature of alay-product advantage. The power factor of the high frequency circuitcan also be corrected to 100% by the condensers, giving a two-step meansof lifting the temperature, both steps of which operate at 100% powerfactor.

In order to avoid the objection of the induction passing' through ortending to pass through the Walls of thin tubing, to obtain theadvantage of increase of iuductance in thecoil when heating tubing ofeither magnet-1c or non-magnetic metal and to heat non-magnetic metalwith lower frequencies than would otherwise be effective, I provide(Figure l0) an iron core 47 preferably of nichrome or of a` steel whichhas a high recallesccnce point. It is located Within the tubing where itis surrounded by thc inductor 4S, which may be, for example, of hollowedge wound copper, water cooled. The iron core may be held Within thepipe hy a Wire extending to the end of the pipe. lVhcthc-i' operatingupon iron or steel pipe or pipe of non-magnetic material the core can beanchored electromagnetically. It can be oated Within the tubing at thispoint by attaching it through wire 40 to an armature 50 held in positionagainst longitudinal movement by a fixe-d solenoidal Winding 51 suppliedwith direct current. When in operation the inductor coil would tend tohold the core against longitudinal movement. The core can be heated to atemperature of about (3750 C. by 00 cycle current and to highertemperatures by higher frequency. It correspondingly heats the tube.This is the more efficient because it heats from the inside and there isno Way of escape of the heat except into the pipe.

l-Vhere the size of the stock is too small for convenient inductiveheating, requiring relatively an excessive frequency, or because of thedesirability of heating a number of Wires or small rods at the same timeor for any other reason, I provide a steel or nichrome mulle 52 (Figures11, 12) which may be used in many different forms. I have shown but two.In one (Figure 1l) the inutile is provided with a plurality of holes 53through which the rods or wires 54 to be heated are passed. The muilecan readily be raised to approximately the temperature of recallescenceby relatively low frequency current and can be raised to a much highertemperature b v high frequency current by means and methods alreadyexplained. The wires can`be passed through the mule continuously orstep-by-step, or can be heated and Withdrawn therefrom.

In Figure 12 I show the coil as surrounding a steel inutile 52 which hasbeen longitudinally split at so that it can be grooved to provide apassage 56 through the muiile. The passage in cross section is muchlonger than it is wide suiting it to the reception of band saWbladematerial or other like strips to be heated as for annealing or temperingiurposes. Obviously as many passages may be used as desired with thepreference, however, that they shall not cut through to the surface.since it is desirable to have the magnetic induction in the steel passcircumferentially about the outlines ot' the passage. The strip can beheated entirely by heat conduction and radiation from the niutlie or itcan be placed where part of the induction passes through it. The mulieform is illustrated because it comes within the broader claims ot' myinvention` notwithstanding that subjcct matter specific to it is takencare of in a separate application. The same is also true of condenserand discharge gap source of sup ily.

I eat insulation is provided between the inutile and the coil.

In all of the forms where a plurality of turns per coil is used, Iprefer to use a single layer coil of edgeivound flattened copper tubingand find water cooling of the tubing very desirable.

In Figure 13 I have shown a plurality of inductor loops 57 in paralleleach capable of being water cooled through pipe connections 5S andconduits 59 and each having a considerable extension aong the length ofthe charge. These loops are shown as having separate .secondaries 6Ucooperating with tl'zc same primary (51 of a transformer fed from anyline G2. (i3 across which the capacity G4 is thrown in condenser form.In order to provide for higher frequency which Will ordinarily bedesirable I show the line as fed from motor generator 65.

In Figure 14 inductor loops from a given secondary 60 are shown inparallel and as edgewound fiattened copper tubes (i6 which require noinsulation between them as they comprise part ot the same turn or loop.differing in this from the edgewound cois such as are shown in Figure10. Not only electric current but the Water flows in parallel throughthese turns. The edgeivise Winding ot' the flattened copper tubing givesa very much larger surface of contact of copper with the cooling Waterthan in the form shown in Figure 13.

In operation upon stock of the character treated herein, whether it besolid or hollow, of uniform or of irregular cross-section, and whether acore or muile be used or not, the coupling increases With increaseddiameter of the stock as the gap required is approximately constant.

The frequency desirable reduces with increase of the diameter or withincreased thickness of the stock since it is desirable not to haveetliective induction extend beyond the center of the stock. This wouldapply also to the center of the core or mule where these are used. Theformula for determining this frequency is 25 X 10""p N- #12p `.vhere Nis the frequency` p the resistivity of the material, p, the permeabilityand 12 is the depth of penetration, approximating one-third of `thedistance to which the induction extends.

The higher frequencies have the advantage of requiringr less capacity tocorrect the power factor, but have the disadvantage of requiring specialgenerators or other equipment to supply the current. With magneticmaterials low frequencies can be used even on relatively small diametersof stock: but when the stock is non-magnetic` unless it be large indiameter, high frequencies must be used if too deep penetration ofinduction into the stock is to be avoided.

My invention is independent of the number of turns per coil and of thedetail ofthe coil and can be applied with loops as distinguished fromturns, With loops.in series or in parallel, with coils, single, inseries or in parallel and with great variety of current supply. I preferto Water cool the coils and where the inductor coil comprises more thanone turn, I prefer to use con.- ductors having one dimensionconsiderably greater than the other in cross-section and with thegreater dimension radial to the axis of the coil, whether the coil bewater cooled or not.

My invention is applicable to magnetic or non-magnetic materials whethersolid or otherwise and to heating of hollow or solid materials directlyby the CZR heat development in the materials themselves. Wholly or inpart. by heat conduction and radiation from a casing or core or InutileWithin which CZR heat is developed.

In operation the material to be heated may be progressed through thecoil or through or about the mutlie, step-hystep or continuously or,much less desrably, may be inserted therein and Withdrawn. Consideringthe continuous operation, by odds the most advantageous form, the objector material to be enough to Le at the proper tem erature at e point ofuse as it emerges rom the final coil or turn. Heatin magnetic materialto the point ai which itegins to lose its magnetism may be eHective at arelatively low 1 frequency though, with small stock, or because of exense of power factor correction, very desira ly at a. frequency higherthan available from line sources of supply and heating beyond therecallescence point will be erformed at a much higher frequency. gVherethe material is non-ma netic and unless assisted by the inclusion omagnetic material in the form of a mullle or core the heating will beperformed wholl at a higher frequency than that of availab e linesources of supply.

n view of my disclosure herein other forms and uses of m invention willundoubtedly occur to those s {illed in the art dilering from mine inadaptation to special uses, suiting the preference or whim of theindividual designer or for the purpose merely of avoiding copying of myforms and it is my purpose to include herein all such as come within thereasonable spirit and scope of what I regard as a very broad invention.

Having thus described my invention what I claim as new and desire tosecure by Letters Patent is 1. In the art of inductive electric heating,a hollow helical coil, a source of hi h frequency electric currentapplied to t e terminals of the coil and means for moving an article tobe heated having much greater len h than width or thickness through thecoi while it is bein subjected to the heating effect of the coil, t ecoupling between the article and the coil being close.

2. In the art of inductive electric heating a plurality of spaced,helical coils having their axes in line, in combination with a source ofhigh frequency electric current applied to the terminals and means formoving a long article to be heated longitudinally through the coils, thecoupling between the article and the coils being close.

3. In the art of inductive electric heating a plurality of helical coilsaxially in line, means for supplying high frequency current separatelyto each coil, comprising an alternatin current circuit and Vconnectionsfrom the circuit to the terminals of the different coils and/means formoving a long article to be heated longitudinally through the coil, thecoupling between the article and the coils bein close.

4. n the art of inductive electric heating, an alternating currentenerator of standard rotaryv type aving a requenc above normal inefrequencies, a plura ity of coils axially in line fed from saidgenerator, means having ca acity, applied across the line to improve t epower factor, means for concontinuous or step-by-ste metal article to beheate t rough the coils to receive successive increments of heat fromcurrents induced by the current passing through the coils, the couplingbetween the article and the coils being close.

5. In the. art of inductive heating, an inductor coil, sources ofalternating currents of different frequency, connections for applyingthe currents through the coil and means for moving a long article to beheated longitudinally through the coil, the coupling between the articleand the coil being close.

rogression of a 6. In the art of inductive electric heating, -s

a plurality of inductor coils axially in line, in combination with meansapplied t the coil terminals for passing current of one frequency throuh all of the inductor coils and means applie to the terminals of onecoil for alpplying a current of different frequency t rough one of saidcoils.

7. In the art of inductive electric heating,

an alternating current supply having commercial frequency, an inductorcoil fed therefrom and an overexcited synchronous motor run by saidcurrent supply connected within the circuit holding the said and adaptedto correct the power factor for said circuit, a high frequency generatordriven by said synchronous motor, a second inductor coil fed from saidgenerator and means having capacity connected in the circuit of thesecond inductor coil for power factor correction for the second circuitand means for passing an electrically conductive article to be heatedthrough said coil to receive successive increments of heat by inductionfrom the current therein.

8. An alternating current supply circuit of commercial frequency, anoverexcited synchronous motor fed therefrom, an inductor coil fed fromsaid current supply in circuit with said motor and whose power factor isadapted to be corrected by said synchronous motor, a generator driven ythe synchronous motor, a second inductor coil in inductive relation withthe same charge as the first, connections from the generator to theterminals of said coil and means having capacity for power factorcorrection for said second coil.

9. A multiphase source of alternating current sup ly of commercialfrequency, a plurality o inductor coils fed therefrom, surrounding andadapted to operate upon the same charge, a synchronous motor driven bysaid multiphase current su ply, a generator driven by the motor, aninductor coil fed from said generator and surrounding the same charge asthe other coils and means effective for power factor correction for theVcircuit of said inductor coil.

10. A multiphase source of alternating current supply of commercialfrequency, a plurality of inductor coils fed therefrom adapted tosurround and operate upon the same charge, a synchronous motor driven bysaid multi-phase current supply, a multi-phase generator driven by saidmotor, a plurality of inductor coils fed from said generator andsurrounding the same charge and means for power factor correction foreach ofthe phases of said circuit.

1l. A multiphase source of alternating current supply of commercialfrequency, a plurality of inductor coils fed therefrom surrounding andadapted to operate upon the same charge, a synchronous motor driven bysaid multiphase current supply, a generator driven by the motor, anddelivering current at a higher frequency than the frequency of the motorsupply, a plurality of inductor coils fed from said generator andsurrounding the same charge, means'for power factor correction -for eachof the phases of said circuit and means for passing a charge through thecoils to receive successive increments of heat by induction from thecurrent therein.

12. In the art of inductive heating, a synchronous motor commercialfrequency current supply therefor, a generator driven therefromdelivering a higher frequency than that of the current supply for saidmotor, a. current supply for the motor, a heating inductor coil to whoseterminals currents of both frequencies are applied.

13. In -the art of inductive electric heating, a plurality of inductorcoils adapted to operate successively on the saine charge, two separatesources of alternating current supply applied to the terminals of thecoils operating at two different frequencies and means for power factorcorrection of electro-magnetic and capacity character respectively forthe circuits of the coils having different frequencies.

14. In the art of electric inductive heating, a heating inductorcomprising spaced hollow helical inductorcoil sections having a comnionaxis, rotary guides located generally in line with the common axis andadapted to support an article to be heated having greater length thanthe width or thickness, so that it may be passed through the hollowcoils, and a common source of hlgh frequency current connected to passthe current through all of the coils concurrently.

15. The method of heating travelling stock which consists in progressingthe stock and coincidently passing high frequency current around thestock with close coupling to heat the circumference of the stock.

16. The method of heating travelling stock which consists in providingthe stock with a definite line of travel and in surrounding the line oftravel at close coupling with high Ifrequency current at intervals alongits length.

17. The method of heating normally ma netic stock which includes movingthe stoc passing about it relatively low frequency current andimpressing high frequency oscillations upon the low frequency currentwhere the stock loses its ma netic properties.

18. The method of eating stock of material magnetic at lowertemperatures and nonmagnetic above a critical temperature which consistsin moving the stock, in passing about it at the same point in its travelboth high and low frequency current and in allowing the proportion ofthe induction in it from the two currents to be determined by thepermeability of the stock.

19. The method of heating traveling stock, which consists in moving thestock and subjecting it to the induction of high frequency currentpassing about the surface of the stock at close coupling therebyconfining the flow of current to a thickness of the stock at the surfaceinversely proportional to the square root of the frequency, increasingthe resistance and reducing the length of stock necessarily within thecoil for a required reslstance.

20. The method of heating travelling stock, which consists in moving thestock and in applying increments of heat to it successively bysuccessive inductions of high frequency current at its surface, thecoupling of the inducing and induced currents being close.

21. The method of reducing the length of travelling stock through whichit is necessary to pass an electric current in order to heat the stockby the PR secondary loss, which consists in increasing the frequency ofthe current above normal and making the coupling with the stock close inorder that the proportion of the cross-section of the stock throughwhich the current actually travels may be reduced and its resistanceincreased.

EDWIN F. NORTHRUP.

CERTIFICATE 0F CORRECTION.

Patent No. 1,900,842. March 7, 1933.

EDWIN F. NORTHRUP.

lt is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows: Page 3,line 25, after "has" insert the word "not"; page 5, line 95, claim 7,for "holding the said" read "including the coil"; and that the saidLetters Patent should be read with these corrections therein that thesame may conform to the record of the case ln the Patent Office.

Signed and sealed this 19th day of September, A. D. 1933.

M. J. Moore.

(Seal) Acting Commissioner of Patente.

